Hydrocarbon storage tank with strengthened roof



Aug. 18, 1953 R. M.' MERCIER HYDROCARBON STORAGE TANK WITH STRENGTHENEDROOF Filed Dec. 17, 1945 '2 Sheets-Sheet l INVENTOK R0 BER M. ME/zc/e zA TTOKNEYS,

Patented Aug. 18, 1953 UNITED STATES ATENT OFFICE HY'DROCARBON STORAGETAN-K WITH STRENGTHENED ROOF responsabilite limite) Application December17, 1945, Serial No. 635,511 In France December 19, 1914 4 Claims.

It is known that hydrocarbons are generally stored in metallic tanks,having the shape of a.

vertical cylinder and provided with a roof in the shape of a calotte ora cone.

The wall and the metallic roof of these tanks are easily permeated byheat and the atmosphere prevailing inside the tank is heated byconvection and radiation due to the fluctuations of temperature andirradiation of the outside atmosphere.

The fluctuations result in a sequence of expansions and contractions ofthe carburated air confined above the liquid fuel to cause an actual intake of air from the exterior and an expulsion of carburated air fromthe tank. To reduce this respiration caused by variations intemperature, it has been proposed to provide the tank with a breathingvalve means in communication with the outside atmosphere when theinternal pressure or vacuum exceed predetermined values fixed inrelation to the resistance of the tanks.

The reductionof vapor loss from the tank thus depends on the pressuresand vacuum for which the valve has been set.

Thus for example, a saving of about 30 per cent is observed if thevacuum is limited to grams per square centimeter and the overpressure tograms per square centimeter, and it would attain 90 per cent, if thetank could resist a pressure variation of from 80 to 100 grams persquare centimeter.

Unfortunately, it is very difficult to construct tanks capable ofresisting these high pressures under such Working conditions, since theintricate feature is the assembling of the dome on the upper part of thecylindrical tank. As a matter of fact, the application of the gaseouspressure to the dome creates in the supporting angle iron assemblyconsiderable compression stresses which are liable to cause said angleiron to collapse and to develop folds in the upper part of thecylindrical wall. This structural difiiculty makes it difficult toconstruct new tanks gauged for 100 gram pressures and makes itpractically impossible to modify existing tanks with heavier sheet metalto permit higher pressures.

It is known that by covering the outside of the dome with a layer of anonconducting material, that the amplitude of variations internaltemperature and consequently the respiration will be reduced.

My invention relates tohydrocarbon storage tanks comprising a metallicbodyof upright cylindrical shape surmounted by a metallic dome assembledwith the cylindrical body by means of a metal ring fitted inside Saidtank,

2 ring is further provided with an outer concrete strengthening eoveringenabling the tank to withstand variations in internal pressure by far inexcess of the values which are permitted in the usual metallicstructures.

According to one embodiment of my invention, said strengthening consistsof an annular concrete girder moulded around and against the outersurface of both the cylindrical body and of the dome of said tank at thelevel of the assembling ring, said girder rigidly adhering to thecylindrical wall of the tank. The girder is rendered rigid with theassembling ring and with the cylindrical wall by a suitable means.

According to another embodiment, the said girder forms an integral partwith a concrete cupola moulded (into the metallic dome and whichcomprises moreover radial trusses assembled on a central cal'otte. Saidtrusses may be interconnected by metallic reinforcements secured to theouter wall of the dome.

In a third embodiment of my invention, the said concrete cupola,constructed to withstand vertical downward stresses, is covered aftersetand hardening by a second concrete cupola of the same shape andadapted to withstand vertical downward stresses due to its weight.

My invention provides also particular means for rigidly uniting theconcrete gird-er with the metallic assembling ring and the vertical wallof the cylindrical body.

Furthermore, my invention provides means permitting the boarding orplanking of the concrete girder to be constructed without the aid ofscaffolding. Means are also provided to in- The above improvements areapplicable to existing tanks or tanks to be constructed.

The improvements which will be described hereinaiter'with reference tothe appended drawings make the invention clearer and indicate the mannerfor' realizing same.

Fig.1 is a vertical section through a metallic tan-k reinforced by meansof an annular concrete girder.

Fig. 2 is a vertical section through a cupola covered metal tankreinforced by an annular girder integral withtheconerete cupola.

i Fig; 3 is a partial plan view' of said cupola.

of a double concrete ilar to that of Fig. 8 and provided with a heat 7insulating means. 7

In the drawings, the tank is represented by its bottom 1, itscylindrical body 2, the roof frame with radial trusses 3 freelysupporting the dome a built up with metal sheets assembled on thecylindrical wall by means of the assembling ring of rectangularcross-section 5. The dome ha in its center the manhole 6.

Referring to Fig. l, the upper part of the tank is encircled at thelevel where the dome is assembled With the cylindrical wall, by areinforced concrete girder 1 whose section of approximately angle ironshape reinforces the angle iron assembling the dome on the cylindricalwall.

Said girder is provided with channels 8 separated from each other by adistance of about one meter permitting the rain water to flow off. Abitumen strip 9 prevents this water from penetrating between theconcrete and the metal sheets of the dome in case it should accidentallyhappen that the concrete becomes detached from the sheet metal.

To construct the girder of reinforced concrete, it will be advantageousto previously subject the dome of the tank to an internal overpressureeither by applying a gas under pressure approximately equal to thenormal working pressure, or by completely filling the dome with Water tosubject the assembling angle iron and the adjacent sheets to acompression stress of the same order of magnitude as that resulting frompressures which the tank is to be exposed to.

In this manner the tank is secured by a hoop to the concrete crown toavoid the detachment from the metal sheet through the action of buildingstresses.

The securing of the crown to the tank is improved by providing carp-tailbolts II], at approximately every 50 cm. of periphery for the rivetsassembling the angle iron with the cylindrical wall. lhe concrete girderstrengthens the head angle iron with which it is rigidly secured by thebolts H for adherence to the metal sheet and the hoop. Owing to itsL-shaped section fitting over the assembling angle iron, the concretegirder effectively counteracts the tendency of the sheet to developfolds which may cause the assembly to collapse.

In the embodiment according to Figs. 2 and 3, the tank is provided witha circular concrete girder H, having an angular section as in theembodiment of Fig. 1. Said girder is rigidly secured to the reinforcedconcrete trusses I 2, l3, 4 etc. assembled on the reinforced concretering l5 in the center of the dome.

Between the trusses which support it, a reinforced concrete hourdis orrubble floor I6 is cast onto the sheet metal of the dome.

This assembly: circular girder, trusses and hourdis ceiling constitutesa reinforced concrete cupola secured to the sheet metal and supportedonly by the vertical wall of the tank. Its adherence to said wall isfurther reinforced by the hemispherical projections of rivet headsimbedded in the concrete during the casting of the latter.

The tank is thus covered with a composite dome consisting of an envelopemade of thin and tight sheet metal which securely adheres to a heavyconcrete cupola to provide the proper resistance to pressure and vacuumwithin the tank and. to transmit vertical stresses to the wall of thetank through the rivet heads 17 (Fig. 4).

As in the case illustrated in Fig. 1, it will be advantageous to buildup the girders and the cupola while submitting the metallic dome to adeformation through over-pressure.

The behaviour of the structure under the stresses is as follows:

- When the tank is submitted to an internal overpressure, the resistanceopposed by the dome is the resultant of the resistance of the dome, ofthe weight of the concrete cupola and of the resistance of the concretecupola. Under these conditions, the deformations of the sheet metal domeare limited to those of the concrete dome, and consequently thedeformations of the head angle iron and of the annular reinforcedconcrete girder are the same. This avoids any separation between thereinforced concrete girder and the vertical cylindrical wall.

When the tank is submitted to an internal vacuum, the resistance of thedome is solely opposed by the reinforced concrete cupola wherein thesheet metal of the dome secured to the concrete fulfills the function ofa reinforcement taking up tensile stresses whether in the case of thegirder or in the case of a hourdis ceiling. The reaction of the latterand of the girders manifests itself through a tensile stress orexpansion of the annular girder and through a vertical stress absorbedby the cylindrical wall of the tank.

The supplementary resistance which the concrete cupola confers to thesheet metal dome permits a very noticeable increase in the limits ofrespiration of the tank as compared with its original structure, and theoperations of transformation and strengtheningv may be effected withoutthe necessity of conducting caldron work or to penetrate the tank.

Moreover, in addition to its resisting action, the concrete hourdislayer acts as a heat insulating covering, reducing to a large extent theeffect of irradiation and the fluctuations in pressure and vacuum causedthereby.

Due to the increase in weight of the tank resulting from the concretecupola, it could be feared that when the tank is almost empty and theinternal pressure forces the bottom to take a spherical shape, that thetank would rise above its foundations. To avoid this accident, a safetydevice is provided to reduce the overpressure to a rate compatible withthe weight of the structure as soon as the pressure attains apredetermined value. This device consists of a tube l8 descending to adetermined level above the bottom and provided at its upper part with avalve I 9. It is obvious that as long as the base of the tube isimmersed, that the respiration will take place through the high-gaugevalve 243 and as soon as the base of said tube is uncovered,j

A warning whistle combined,

with, the valve. [9, is provided, to, indicate a m ximum value oflow-pressure which is not very economical.

As explained hereinbefore, the, strength of the concrete cupola absorbsall of the. stresses. and consequently the original skeleton of the tankno longer fulfills this; use.

If this method of building is applied to. new tanks, it is thereforeadvantageous to replace the classical trusses of the. dome with the typeof reinforcement shownv in Fig. 5

This reinforcement to strengthen the structure consists of L- or T-ironsshown at 2| in- 5. Said irons are disposed like common rafters on theoutside of the dome and welded onto the latter. Holes 22 provided in thevert-i cal flange or web ensure a supplementary adherence of theconcrete. The sectional rafters are imbedded in the concrete girders andnot in the hourdis ceiling.

When the natural adherence should be found deficient, the connectionbetween the concrete of the reinforcement girder and the sheet metal ofthe tank may be strengthened in the manner shown in Fig. 6, by means ofscrews 23, made of medium hard and preferably cement steel. Said screwshave a slightly conical shape and are screwed into the rivet holes. Toput these screws in place, it suffices to cut the head 24 on the riveti'l interconnecting the elements 2 and 5, to expel the rivet toward theinterior of the tank and to forcibly drive the screw 23 into the holethus uncovered. The conical shape of the screw 23 and the hardness ofits metal enable said screw to cut therein its own thread in theelements to immobilize therein in a tight manner.

The screw thus fixed in the sheet metal and subsequently imbedded in theconcrete ensures the rigid connection between the concrete and the sheetmetal. Under normal conditions, the screws thus set in place aresubmitted or subjected, to. shearing stresses, but. they may also besubjected to tensile. stresses. The use of such screws does away withthe necessity of penetrating into the interior of the tank, obviatingthe fixing of nuts therein or the piercing of holes. Moreover, there isno intricate use of taps nor is it necessary to employ heat for theelectric welding of splinters or the like. This means even permitsadhesive pieces to be secured to tanks in service or still containingtheir gaseous atmosphere, without there being any risk of inury.

Finally, the tapered shape of the screw permits the latter to beadjusted to holes of different diameters without afiecting itstightness. Fig. 7 shows a means permitting the boarding to be mounted onthe tank for the purpose of moulding the reinforcement girder. Thebottom 25 of said boarding is carried at certain intervals by chairsupports made of round bars of suitable diameter. The two legs 26 and 21extending throughout the bottom 25 support the boarding through themedium of nuts 28 and 29.

The lateral side 30 of the boarding is held in place by wooden blockswhich render it rigid with the bottom of the mould, and by round ironbraces 32 fitted with nuts 33 which connect it rigidly with the tank.

The legs 26 and 2'! as well as the braces 32 are suspended on the upperangle iron 5 of the tank by means of screws 23 driven vertically downinto the sheet metal ofthe dome and into the next angle iron by themethod mentioned with reference to Fig. 6.

After casting. setting and; hardenin of the concrete, the boarding isreleased by unscrewin the nuts 28., 29; and 33, while the chairs andbracings as well as their anchoring screws 23 remain imbedded in thestructure.

This device avoids the use. of poles, stays and scaffoldings resting onthe ground. The cost of this conventional equipment. is. very high incase the work has to be. done at a height of H] to IE meters.

Fig. 8 shows a manner of constructing the concrete cupola which permitsincreasing the reinforcement limits. of the dome.

It. is well known that the thickness and hence the strength of theconcrete dome depend on the resistance of the sheet metal dome whichserves as a base for the boarding and which is to withstand the weightof the concrete employed at the time of casting.

Practice has shown that. the limit of thickness compatible with saidresistance is of the order of 10 cm.

To obtain a reinforcement of larger thickness without it being necessaryto brace the sheet metal dome of the, tank by means of poles or internalskeletons, the method according to my invention should be carried out inthe following manner:

Onto the wall 2 and the dome 4 are cast a girder l and a cupola l6identical to those described before, but more particularly constructedto withstand vertical downward stresses. After the setting of this firstconcrete casting to the necessary strength, another girder 34 andanother cupola, 1B are cast so as to adhere to the first concretecasting.

This second cupola may eventually be con nected to the first cupola withiron bars, or, a reinforcedconcrete hourdis ceilingmay be provided witha proper resistance to overpressure and vacuumstresses which it willtransmit to its own lateral girder and to the girder of the firstcasting with which it will be rigid, or a nonreinforced concretecastingmay be provided which is opposed by its own weight accounting forthe vertical downward stresses.

It is to be noted that the second nonreinfcrced concrete cupola may beemployed to counterac the tendency causing the bottom of th tanto getout of shape under the action of overpres sures, without trying toobtain any increased resistance of the dome to internal pressures.

Fig. 9 illustrates a means for improving the heat insulating qualitiesof concrete cupolas. It involves the application of a reinforcedconcrete coat '5, Hi of the type described with reference to Fig. 2.After this coat has hardened, tubular bricks are disposed on the surfaceof said coat. Said tubular bricks have triangular sections 36, 3] ortrapezoidal sections 33, 39 or rectangular sec tions 46, M. A layer ofreinforced or nonreinforced concrete G2 is finally cast over saidtubular bricks.

It will be understood that the tubular bricks retain air within theircavities in order to form a heat insulating screen between the externalwall and the dome of the tank.

The us of the above mentioned coating permits this kind of heatinsulating to be improved, since in those applications made to insulatethe domes of tanks, the eificiency was reduced by reason of the feebleweight of the heat insulating material compatible with the resistance ofsheet metal domes.

The device shown in Fig. 9 permits one therefore to combine: thereinforcement of the domes of tanks against the action of overpressureand vacuum, the heat insulating by means of tubular bricks containingair and finally the increased Weight of the tank which is necessary tocounteract the tendency of the bottom to get out of shape under theaction of overpressure.

What I claim is:

l. A reservoir of the type used for storing hydrocarbons comprising avertical cylindrical metallic wall, a metallic air-tight roof, a coverof reinforced concrete poured upon the external face of said metallicroof and adhering to said roof for reinforcing said roof againstinternal subpressures and superpressures, a reinforced concrete beamring molded upon the exterior wall of the upper portion of saidcylindrical metallic Wall to which said reinforced concrete cover isconnected,

said ring being designed to'absorb radial forces which are transmittedto it by the reinforced concrete cover under the influence of internalsuperpressures and subpressures and to secure the fixing of the concreteassembly upon the metallic cylindrical wall, solely by adherence of theconcrete to the metal and by the surrounding in concrete of the naturalruggedness of the metal and the heads of the rivets, the entirestructure being calculated and carried out in such a way that themetallic wall of the roof no longer has to intervene particularly in theresistance of the structure to the effects of internal subpressures and.superpressures.

2. A metallic reservoir according to claim 1 in which the metallic roofcomprises an exterior sustaining frame formed by girders secured uponthe roof and whose vertical leg is perforated and roughened in such amanner that these girders serve to sustain the wall of sheet meta1during the pouring of the concrete and then concurrently improve theadherence of the girders and the concrete cover to the sheet metal roof.

3. A metallic reservoir according to claim 1 wherein supports aredisposed in order to resist forces directed downwardly, and a secondlayer of concrete is poured adheringly upon the upper face of saidconcrete cover serving to set and sup- 4 port said second layer.

4. A reservoir of the type used for the storing of hydrocarbonscomprising a vertical metallic cylindrical wall, a metallic airtightroof, a reinforced concrete cov'er upon the external face of saidmetallic roof adhering to said roof and reinforcing it against theefiects of internal subpressures and superpressures, a reinforcedconcrete beam ring upon the exterior Wall of the upper portion of saidmetallic cylindrical Wall of said reservoir connected to said reinforcedconcrete cover, said ring beam absorbing radial forces transmitted to itby said reinforced concrete cover under the influence of internalsuperpressures and subpressures and securing the fixing of the concreteassembly upon said metallic cylindrical wall solely by adherence ofconcrete to the metal and surrounding in the concrete unevennesses andrivets so that the metallic wall of the roof does not interveneparticularly in the resistance of the structure to the effects ofinternal subpressures and superpr-essures and steel elements located inthe rivet holes projecting into the concrete to improve the assemblageof the latter upon the sheet plate and to improve the adherence.

MERCIER, ROBERT ltlAURICE.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Engineering News-Record, page 555, April 16, 1936.

